CANON XVI -- If any one saith, that he will for certain, of an absolute and infallible certainty, have that great gift of perseverance unto the end, unless he have learned this by special revelation; let him be anathema.

If we cannot say with "absolute and infallible certainty" that we will go to Heaven, how could we possibly make such a claim about any non-Catholic, whether such an individual has been publicly baptized or not??? Clearly, BoD is not visible!

Of course, the Second Vatican Council reaffirmed the decrees of the Council of Trent in Lumen Gentium, 51.

Yes, if the Holy Office letter did, in fact, imply that, but clearly, as the Holy Office cited the Council of Trent, then it could not be implying that BoD was visible, for it would have contradicted Trent, and hence, itself for having cited Trent as an authority!

Agreed!The Letter mentions the dogma and refers to 'the infalllible teaching'.So this was Mons.Fenton's interpretation of the Letter of the Holy Office 1949 with allegedly known exceptions. Visible to him!